subdural hematoma
In this type of hematoma, a blood vessel (usually a vein) bursts in a space just outside of the brain. Blood begins to pool along the surface of the brain, between membranes that cover the brain. Because subdural hematomas arise from low pressure venous bleeding, it may take some time for symptoms to appear after the injury. By contrast, an epidural hematoma, which is blood bleeding between the skull and a tough membrane normally firmly attached to the skull, called the dura mater, usually arises from an artery torn by a skull fracture. The higher pressure arterial blood accumulates much more quickly, usually resulting in a rapid appearance of symptoms (e.g., headache, paralysis, disturbance of consciousness).